Tiny crystals and nanowires could join forces to split water

A scanning electron microscope image, with color added, shows
vanadium oxide nanowires coated with tiny semiconductor crystals
called quantum dots. This combination of materials has shown
promise for splitting water into oxygen and hydrogen fuel, which
could be used to power cars, buses, boats and other modes of
transportation. Image: Christopher Milleville

Published
October 18, 2016

Scientists are pursuing a tiny solution for harnessing one of
the world’s most abundant sources of clean energy: Water.

By marrying teeny crystals called quantum dots to miniature
wires, the researchers are developing new materials that show
promise for splitting water into oxygen and hydrogen fuel, which
could be used to power cars, buses, boats and other modes of
transportation.

“Hydrogen is seen as an important source of green energy
because it generates water as the only byproduct when it’s
burned,” says UB chemist David Watson, one of project’s
lead researchers. “The hybrid materials we’re
developing have the potential to support the cheap and efficient
production of hydrogen gas.”

Watson, professor and chair of the Department of Chemistry,
College of Arts and Sciences, has received a $550,000 grant from
the National Science Foundation (NSF) to pursue the work. UB
physics professor Peihong Zhang, is also a partner on the research,
which is part of a larger $1.4 million NSF-funded project that
teams UB with Texas A&M University, Binghamton University and
Rensselaer Polytechnic Institute to develop the new catalysts for
splitting water.

The project is funded through the NSF’s Designing
Materials to Engineer and Revolutionize our Future, which supports
the White House’s Materials Genome Initiative for Global
Competitiveness by accelerating the discovery of new materials.

A reaction powered by the sun

“The hybrid materials we’re developing have the potential to support the cheap and efficient production of hydrogen gas.”

David Watson, professor and chair

Department of Chemistry

The materials under development are catalysts designed to
harvest sunlight to drive the chemical reaction that divides water
into oxygen and hydrogen.

They are formed from miniscule wires of vanadium oxide that are
combined with various metal ions, then glazed with a coating of
semiconductor quantum dots.

When they’re exposed to the sun, these hybrid materials
generate two critical ingredients for splitting water: a
free-floating electron and what chemists call an electronic hole
(the absence of an electron where there would normally be one).
Both the electron and the hole are used in the multi-step chemical
reaction that converts water into oxygen and hydrogen gas.

So far, the research team successfully created materials that
efficiently produce and separate both a free electron and a hole,
though the scientists have yet to demonstrate that their hole can
be used successfully in the water-splitting reaction.

From an industry perspective, the nanowire-quantum dot approach
has benefits. Both the nanowires and quantum dots can be easily
produced in large quantities from materials that are abundant in
the crust of the earth, and both are “tunable,” Watson
says. As he explains, changing the size of the quantum dots alters
their electronic properties, as does combining the vanadium oxide
nanowires with new materials. This makes it possible to tweak both
components to maximize their efficiency at leveraging sunlight to
split water.

“It’s a very flexible approach — a versatile
platform for converting sunlight and water into fuel,” Watson
says.

The scientists will use the new NSF funding to support an
exploration of the best combinations of quantum dots and nanowires.
In concert with synthesizing new materials, they will
computationally predict which structures will have the best
electronic properties.

“We are trying to put together some fairly complex
machinery to mimic photosynthesis performed by plants, which use
sunlight to split water and make energy. The machinery will be
built from these nanowire and quantum dot blocks, using them almost
as Legos,” says Sarbajit Banerjee, professor of chemistry at
Texas A&M University. “Calculations performed on
supercomputers will guide us on how to rapidly put these blocks
together.”

The research was seeded
by a Scialog grant from the Research Corporation for
Science Advancement, an Arizona-based foundation devoted to the
advancement of science.